1. Field of the Invention
The present invention relates generally to electromagnetic energy radiation and reception, and especially relates to electromagnetic energy radiation and reception effected using impulse radio energy. Still more particularly the present invention provides an antenna with an adjustable-impedance feed that is suited for broadband energy radiation and reception, and particularly well suited for broadband energy radiation and reception employing impulse radio energy.
2. Related Art
Recent advances in communications technology have enabled an emerging, revolutionary ultra wideband technology (UWB) called impulse radio communications systems (hereinafter called impulse radio).
Impulse radio was first fully described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents include U.S. Pat. No. 5,677,927 (issued Oct. 14, 1997) to Fullerton et al; and U.S. Pat. No. 5,687,169 (issued Nov. 11, 1997) and U.S. Pat. No. 5,832,035 (issued Nov. 3, 1998) to Fullerton. These patent documents are incorporated herein by reference.
Uses of impulse radio systems are described in U.S. patent application Ser. No. 09/332,502, entitled, xe2x80x9cSystem and Methodfor Intrusion Detection Using a Time Domain Radar Array, xe2x80x9d and U.S. patent application Ser. No. 09/332,503, entitled, xe2x80x9cWide Area Time Domain Radar Array, xe2x80x9d both filed Jun. 14, 1999, both of which are assigned to the assignee of the present invention, and both of which are incorporated herein by reference.
Earlier-filed applications relating to impulse radio antenna arts include U.S. patent application Ser. No. 09/652,282, entitled, xe2x80x9cSemi-Coaxial Hornxe2x80x9d, filed Aug. 30, 2000; U.S. patent application Ser. No. 09/670,972, entitled, xe2x80x9cElectromagnetic Antenna Apparatusxe2x80x9d, filed Sep. 27, 2000; U.S. patent application Ser. No. 09/753,243, entitled, xe2x80x9cPlanar Loop Antennaxe2x80x9d, filed Jan. 2, 2001; and U.S. patent application Ser. No. 09/753,244, entitled, xe2x80x9cSingle Element Antenna Apparatusxe2x80x9d, filed Jan. 2, 2001.
Basic impulse radio transmitters emit short pulses approaching a Gaussian monocycle with tightly controlled pulse-to-pulse intervals. Impulse radio systems typically use pulse position modulation, which is a form of time modulation where the value of each instantaneous sample of a modulating signal is caused to modulate the position of a pulse in time.
For impulse radio commnunications, the pulse-to-pulse interval is varied on a pulse-by-pulse basis by two components: an information component and a pseudo-random code component. Unlike direct sequence spread spectrum systems, the pseudo-random code for impulse radio communications is not necessary for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Instead, the pseudo-random code of an impulse radio system is used for channelization, energy smoothing in the frequency domain and for interference suppression.
Generally speaking, an impulse radio receiver is a direct conversion receiver with a cross correlator front end. The front end coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The data rate of the impulse radio transmission is typically a fraction of the periodic timing signal used as a time base. Because each data bit modulates the time position of many pulses of the periodic timing signal, this yields a modulated, coded timing signal that comprises a train of identically shaped pulses for each single data bit. The impulse radio receiver integrates multiple pulses to recover the transmitted information.
Antennas having ultra-wide band (UWB) properties are desired for a variety of applications, including impulse radio applications for communications, positioning, and other uses. Historically the principal use of UWB antennas has been in multi-band communication systems. Such multi-band communication systems require an ultra-wide band antenna that can handle narrow band signals at a variety of frequencies.
The recently emerging impulse radio communications technology often referred to as impulse radio has placed different, more stringent requirements on antenna performance. Impulse radio communications uses UWB signals, so an antenna for use in an impulse radio system must transmit or receive (or, transmit and receive) over all frequencies across an ultra-wide band at the same time. Thus, ultra-wide band impulse radio requires that an antenna performs well over ultra-wide bandwidths, but is also non-dispersive of those signals. It is desirable in such UWB impulse radio systems to have an antenna with a phase center that remains fixed as a function of frequency so that radiated and received waveforms are not distorted.
Many of the known UWB antennas do not meet this requirement. The most frequently used class of UWB antennas is a xe2x80x9cself similarxe2x80x9d frequency independent antenna, such as a log periodic antenna or a spiral antenna. Such antennas rely on a smaller scale portion to radiate higher frequency components, and a larger scale portion to radiate lower frequency components. As a result, different frequency components are radiated from different parts of the antenna, and resulting radiated waveforms are distorted. The distortion thus created can be corrected and compensated for by a variety of techniques known to artisans skilled in radio frequency (RF) design and signal processing. However, such corrective measures and structures add unnecessary complications and expense to overall system design.
Horn-type antennas can be non-dispersive, but they tend to be large, bulky and highly directive. Small element antennas are known, such as bow-tie antennas, but they tend to have excessive reflections that can be offset only by resistive loading. Resistive loading is a lossy solution that minimizes reflection at the cost of lowering radiation efficiency. Non-resistive loaded small element antennas have been disclosed in U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. These antennas emit a short non-dispersive pulse, but tend to have significant reflections and less than desirable impedance matching.
There is a need for a small omni-directional antenna that can radiate energy efficiently with minimal reflection and distortion.
In particular, there is a need for a small omni-directional planar dipole antenna that can radiate energy efficiently with minimal reflection and distortion.
An apparatus for establishing signal coupling between a signal supply and an antenna structure that includes a first radiating element and a second radiating element. The signal supply delivers a signal to the antenna structure at a connection locus. The first radiating element has a first proximal edge and a first distal edge with respect to the signal supply in an installed orientation. The second radiating element has a second proximal edge and a second distal edge with respect to the signal supply in the installed orientation. The connection locus generally includes a portion of the first proximal edge and the second proximal edge. The apparatus includes: (a) a first feed structure extending a feed distance from the signal supply in the installed orientation to the second proximal edge. The first feed structure substantially divides the first radiating element into at least two electrically common lands in spaced relation with the first feed structure to establish a separation distance intermediate the first feed structure and the at least two lands on two sides of the first feed structure substantially along the feed distance. (b) a second feed structure coupling the signal supply with the first proximal edge. The separation distance is dimensioned appropriately to establish a signal transmission structure between the at least two lands and the first feed structure. The geometry of the signal transmission structure may be varied along its length so as to establish a desired impedance transformation intermediate the first and second feed structures.
It is therefore an object of the present invention to provide a small omni-directional antenna that can radiate energy efficiently with minimal reflection and distortion.
It is a further object of the present invention to provide a small omni-directional planar dipole antenna that can radiate energy efficiently with minimal reflection and distortion.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.